Sometimes Windows can be clogged with speed-sapping software or even malicious programs. If this happens, your best bet is to wipe the slate clean and reinstall Windows afresh.
How you achieve this depends on the company that assembled it. Custom-built desktop PCs and laptops from smaller system builders may well include a Windows installation DVD, but if your PC comes from the likes of Lenovo or HP, you'll need to follow a different process that will reset your computer to its original factory settings.
Hidden on your hard drive is something called a drive image. This is an exact copy of the Windows configuration installed on your computer when it was new, which can be copied over the damaged Windows data with the aid of some clever system recovery software.
Power up your PC and tap [F8] until a menu titled Advanced Boot Options appears. Select the 'Repair your computer' link at the top of the list and press the [Enter] key. You may find your computer's recovery software starts up straight away. If not, continue through a language and keyboard preferences screen to the point where you're required to select your usual Windows username and enter the corresponding password if necessary.
You'll now be met with a menu titled System Recovery Options. The last link is usually the one to activate the computer manufacturer's recovery software.
On a Dell machine it's likely to be labelled Dell DataSafe Restore, HP call its software Recovery Manager, and Sony's version comes under the heading VAIO Recovery Center.
The most straightforward way to restore a big-brand PC such as a Dell or HP machine to its factory settings is to use the preserved copy of Windows that you can find tucked away in the depths of your hard drive.
But what if this copy of the operating system has become damaged or deleted by a virus or some other malicious software?
Fortunately, it's likely that your computer came bundled with one or more system recovery DVDs as a backup for the content stored on your hard drive. Inserting the correct disc and accessing it by pressing [F12] at start-up should kick off the same factory reset process as described in the previous page.
Download the files
Sometimes PC manufacturers like to save a few pennies and, rather than include these discs as standard, they ask you to burn your own when you first log on to your PC.
If, like us, that all seemed far too tedious to you at the time and you didn't bother, most system builders will send you replacement recovery discs. However, the cost and hassle involved in obtaining these varies considerably between companies, so if you don't fancy jumping through potentially expensive hoops, check out the manufacturer's website where they hopefully host an image you can download.